It's rather clear to me that ole Howie Stern, the lawyer that doesn't work ... ONLY wanted her money. Anna was the breadwinner for ALL of them. BUT with mega millions in the wings, why bother to put up with her? So he didn't. He murdered the kid through drugs and now his mother. He's getting away with murder not once but looks like twice. He was emboldened. Hope the baby doesn't have some "tragic accident" too ... . What's a man going to do with a baby that most likely is NOT his?
I suspect Stern looked at Anna's family situation, especially the disturbing presence of 20 year old Daniel, who, between his drug binges, could see what Stern was, and decided to eliminate Daniel. Daniel, being a whacked out druggie, was a sitting duck for a lethal OD of any number of substances that could not be traced to Stern under circumstances where Stern couldn't raise a reasonable doubt about the drugs' provenance.
IMHO, having done Daniel so effectively, Stern then turned his attention to the even more drugged up and neurotic Anna and untraceably provided just the little bit of extra juice needed to bump her off. Now, if he's declared the baby's father or can produce a will that makes him Anna's beneficiary, he can cut a deal, settle Anna's lawsuit, and walk off with 20 or 30 million dollars.